We propose to investigate the role of intracellular proteinases in the metabolism and differentiation of yeast cells. Mutants defective in known proteinases or in proteolytic processes have been and will be isolated and characterized. The effects of deficiency for the proteinase or proteolytic system on the biological and biochemical characteristics of the cells will be determined. Cellular processes to be scrutinized include cell growth and division, meiosis and sporulation, and protein degradation induced by starvation, sporulation or medium change. Mutants unable to degrade unstable proteins will be characterized for the spectrum of proteins rendered stable by the mutations (nonsense fragments, thermolabile enzymes, gluconeogenic enzymes upon medium shift, etc.)